Egg & Embryo Freezing Q & A
by Sam Najmabadi, MD
What is Cryopreservation?
Cryopreservation is a technologically advanced method to preserve and save harvested eggs or embryos for future use. This process is often used in conjunction with IVF or if a woman wants to preserve her eggs to improve her chances of having children later in life. IVF can result in more viable embryos than can be injected at one time. When this happens the remaining embryos are frozen and stored for future use. The aim of this procedure and service is to store the embryo cryogenically and to maintain its viability for the future. For example, some IVF children could have younger siblings which were technically conceived at exactly the same time, but not implanted until years later due to the increased success of embryo cryopreservation.
What happens during the procedure?
When a large number of eggs are harvested the patient can either have the eggs frozen, or fertilized. If she chooses fertilization, some of the embryos will be implanted to her uterus as part of the IVF procedure. Any additional embryos are preserved for future attempts to have children. One of the processes available to freeze the embryos is called vitrification, which is essentially flash freezing the embryos in a matter of seconds. This technique can increase the chances of implantation in the future by eliminating opportunities for damage to occur to the embryo.
What kinds of technologies are available for freezing eggs or embryos?
There are now two types of freezing technologies that are used in IVF laboratories. The difference is the speed at which the embryos are frozen. The older technology is called slow freezing and the second, newer technology is called vitrification.
When the slow freezing method is used to preserve eggs and embryos, the freezing requires the removal of water from the individual cells of the embryo. If water remains, it forms crystals which can disrupt the inside of the cells or cut through the outer layer of the cells. A cryoprotectant is added to the cells which replaces most of the water inside the embryo. Under the correct conditions, the cryoprotectant does not form crystals and the embryo can safely withstand cryogenic storage.
Vitrification flash freezes the embryos or eggs. The embryos are submerged into liquid nitrogen at roughly minus 200 degrees. This process does not allow time for crystals to form and assume a glass-like state. Embryo survival after vitrification has significantly improved to 98% from approximately 70% after slow freezing.<
How successful is this procedure?
The success rates for an egg or embryo surviving the freezing and thawing process are higher using the newer vitrification technology and are closer to the success rates of using fresh embryos for implementation. The embryology team at the Center for Reproductive Health and Gynecology has extensive experience with the technique of fertilizing previously vitrified eggs. They have achieved egg survival rates of approximately 80%, fertilization rates of over 80%, and pregnancy rates above 50%.